Fluid enhanced ablation therapy involves the introduction of a fluid into a volume of tissue to deliver a therapeutic dose of energy in order to destroy tissue. The fluid can act as a therapeutic agent delivering thermal energy into the tissue volume—thermal energy supplied from the fluid itself (e.g., a heated fluid) or from an ablation element that provides thermal energy using, e.g., radio frequency (RF) electrical energy, microwave or light wave electromagnetic energy, ultrasonic vibrational energy, etc. This therapy can be applied to a variety of procedures, including the destruction of tumors.
One example of fluid enhanced ablation therapy is the ablation technique described in U.S. Pat. No. 6,328,735, which is hereby incorporated by reference in its entirety. Using the ablation technique described therein, saline is passed through a needle and heated, and the heated fluid is delivered into a target volume of tissue surrounding the needle. In addition, RF electrical current is simultaneously passed through the tissue between an emitter electrode positioned on the needle and a remotely located return electrode. The saline acts as a therapeutic agent to transport thermal energy to the target volume of tissue via convection, and the RF electrical energy can act to supplement and/or replenish the thermal energy of the fluid that is lost as it moves through the tissue. The delivery of thermal energy via the movement of fluid through tissue can allow a greater volume of tissue to be treated with a therapeutic dose of ablative energy than is possible with other known techniques. The therapy is usually completed once the target volume of tissue reaches a desired therapeutic temperature, or otherwise receives a therapeutic dose of energy.
Fluid enhanced ablation therapy can have a number of advantages over, e.g., conventional RF ablation techniques. For example, the delivery of fluid in combination with RF energy can more effectively convect the heat developed near the RF electrode into the surrounding tissue. This can prevent tissue adjacent to the RF electrode from charring and desiccating due to the accumulation of too much thermal energy near the electrode. In conventional RF ablation, this charring can occur in tissue near the electrode even after only a short amount of time. Tissue charring can be problematic because it is accompanied by an increase in tissue impedance that can prevent the transmission of RF energy through the tissue, thereby effectively ending the therapy. Localized overheating of tissue can also cause so-called “steam pops,” which are explosive phase changes of liquid contained in tissue. If the fluid has a higher conductivity than the surrounding tissue, the volume rate of deposition of RF energy immediately adjacent to the RF electrode can be reduced somewhat, further decreasing the risks of charring and desiccation adjacent to the RF electrode.
As a result, it is desirable that fluid be delivered into tissue wherever RF or other ablative energy is being delivered. References such as U.S. Pat. No. 6,328,735 contemplate delivering fluid throughout an RF energy field, however, it has been discovered that the devices described therein do not actually produce the desired uniform fluid distribution field. Rather, as explained in more detail below and illustrated in FIG. 3, fluid is delivered only from a distal end portion of the device. Moreover, in other devices fluid is intentionally delivered only from a distal-most end of the device via, for example, a single opening at a distal end of the device or a plurality of openings positioned at or adjacent to a distal end of the device. In such devices, an electrode or other energy delivery element often extends proximally from the one or more openings and there can be a misalignment between the RF or other energy field and the fluid distribution field. Regardless of the particular configuration of a device, a lack of fluid delivery along an entire length of, for example, an ablation electrode or other portion of a device intended to deliver thermal energy and fluid can reduce the effectiveness of the therapy and lead to potential complications for a patient.
Accordingly, there is a need for improved devices and methods for delivering fluid to tissue during ablation therapy. More particularly, there is a need for new devices and methods for ensuring that fluid is delivered in a desired distribution from a plurality of outlet ports during an ablation procedure, such as fluid enhanced ablation therapy.